Most Features you might be missing can be installed with commodities.
The desktop and window manager should be replaced, trying to fix old software seems pretty pointless to me (in this case).
As for speed - on comparable hardware you won´t find anything that is faster than Workbench.
Doesn't mean a faster gui system isn't possible.
What is your favorite WM?
I don't really have one! I'm just complaining about the AOS gui lagging behind, while this isn't necessary from a technical viewpoint.
But neither KDE nor GNOME nor Windows nor Mac OS let you even control the Z-order of your windows properly. You can´t tell Windows to open two files of the same type with different programms. You can`t leave out icons on your desktop or snapshot a window or icon.
Those are nothing but flaws in those gui systems, and there's no reason why we can't have a gui system that does it all right.
All this is just on Workbench and I bet if someone implements "modern" features into Workbench, he is going to break some of the old stuff. Why not let these be commodities?
Better to replace Workbench.
I don´t get your meaning of "modern" anyways. Or do you mean multitouch?
No, I mean far less limited than what's available for AOS. Mui is a nice attempt, but can still be done better, and certainly faster.